Large metal plate on transom

[bjanakos]

I removed the swim platform mounts on my transom and re-purposed the holes to install underwater lighting. just off-center to port there is a metal plate mounted to the transom below the water line. it is about 16" x 8" or so. It looks like it's been there since the boat was built because there was no bottom paint behind it.

I removed it to have access to install the light, and also prep the area since I am refreshing the bottom paint. I am curious if it is a zinc plate (its non ferrous), but it just "feels" more like aluminum. There is a green wire attached to the studs on the inside, so I am wondering if this is sacrificial metal, or would this be some sort of grounding plate? I am on Lake Michigan, so I really don't need zinc, so I want to know if this can be eliminated.

[prowlersfish]

Could be a ground plate used back in the Pre Vhf days ( am 2 way raido ) also aluminum is used instead of zinc in fresh/brakish water some times ( don't mix )

Update ; The aluminum is used is salt as a replacement for zinc and recommend for brackish water . It is also list for fresh but I believe magnesium would work much better .

[Paul]

Could be a ground plate used back in the Pre Vhf days ( am 2 way raido ) also aluminum is used instead of zinc in fresh/brakish water some times ( don't mix )

Back in the day, I used to have a LORAN that needed to be grounded in this manor.

[gitchisum]

If it looks like this Bill, it's a grounding plate like Paul stated.

grounding plate.JPG (90.17 KiB) Viewed 8781 times

[bjanakos]

Yes, it looks like that!

And it also had a loran on there at one time. Is there anything other than that radio that grounds to it? I notice that my rudders are also wired up. I may put a 10 meter radio in the boat, so it would come in handy.

Thanks for the info.

[jimbo36]

Sounds like a Dyna Plate, your electrical ground.

[prowlersfish]

Could be a ground plate used back in the Pre Vhf days ( am 2 way raido ) also aluminum is used instead of zinc in fresh/brakish water some times ( don't mix )

Back in the day, I used to have a LORAN that needed to be grounded in this manor.

Your showing your age . I believe Loran A used a ground plate ( opps showing my age now )

[Paul]

Your showing your age . I believe Loran A used a ground plate ( opps showing my age now )

It's OK for me to show my age as long as my boat doesn't.

[Stripermann2]

Also known as a Diver's Zinc. I too had a Loran when I purchased the boat.

[prowlersfish]

Also known as a Diver's Zinc. I too had a Loran when I purchased the boat.

I did not scroll down the pic , but now that I did I agree that's a zinc

[K4282]

Slightly off topic what did you install for underwater lights, I put 5 lumitech seablaze 3 on my first F32, I just put 4 Macris lights on my new one

[captainmaniac]

The right material for sacrificial anodes depends on the type of water you operate in.

"Borrowed" this from West Marine:

• Zinc or aluminum for salt water: If you are a saltwater boater, you should install zinc or aluminum anodes to prevent galvanic corrosion on the engine and underwater parts of your boat.
• Magnesium for fresh water ONLY: Since fresh water is much less conductive than salt water, magnesium anodes are the best choice because they’re more active (less noble) than zinc or aluminum so they will protect your engine parts more effectively. Caution: do not use magnesium anodes in any application other than fresh water because they will corrode rapidly, exposing your boat and engine to possible damage.
• Aluminum for brackish water: More active than zinc, aluminum anodes are a good compromise where fresh and salt water mix, such as the brackish water of river deltas, or if you use your boat in a variety of water types. Zinc is too passive for brackish water, where it gets covered in a zinc oxide film and becomes inactive. Magnesium corrodes too rapidly (due to the water’s salt content), leaving your boat without adequate protection.

Blows my mind that most marine suppliers around me only stock Zinc... I am on Lake Ontario... nobody here needs zinc... they need Magnesium. I challenged the owner of one store about what they stocked, and he said that most people walk in to the store (after reading US based magazines) and say they need a zinc anode... so they stock and sell zinc instead of telling the customer they are wrong, and they need Magnesium... When they told customers that, the customers went elsewhere to buy (useless)zinc anodes. The store initially stocked Magnesium, but nobody would buy it because they "knew" they needed zinc. Easier for the stores to give people what they want, than what they need... grrrr

One final point is that you might need sacrificial anodes for reasons other than you are thinking about... If a nearby boat at your marina has an electrical issue, that can lead to a flow of current from their boat to whatever ground it can find (which may be your boat). Your anodes may be eroded by a bad ground on boats near you, or electrical cables in the water near you. Better to have an anode erode than the galvanic corrosion eating away at your rudders or props!

Don't just assume that you don't need protection because you are on Lake Michigan... All boats need protection. If you or anyone near you uses electric power, you need protection.

[Big D]

Not all transom plates are used for grounding, some are there as anodes only.

I agree with CM's comments. The store however is not doing their customers any service by selling them zinc. I absolutely refuse to sell or install zinc. I find once you take the time to properly educate the consumer, they will make the change even though it’s more expensive and has to be done every one or two years. If they have to, it`s very easy to take the customer online at the store and show them the numerous sites that confirm they should be using magnesium. I always get a kick out of people that tell me their anodes have been on their boats for 10 years or more. That right there should tell them something; if they last long, they aren’t doing their job! They’re called “sacrificial” for a reason! Not to mention that after a very short time in fresh water, zinc gets a thin coating on its surface that renders it useless. It’s sometimes noticeable as a slightly yellowish tinge if I recall. The challenge is getting everybody in a marina to make the switch so that the ones that do aren’t sacrificing for their neighbours. The other thing that should be noted is that zinc is not good for the environment hence the movement to do away with them period.

[prowlersfish]

Not all transom plates are used for grounding, some are there as anodes only.

The other thing that should be noted is that zinc is not good for the environment hence the movement to do away with them period.

There has been some call for aluminum "zincs "in salt water in some states . I have a set for my boats running gear . But I have not switched as I have none for the Engines or gen and you not suppose to mix them . And wonder about using them when every one else is using real zinc .


Big D . My Northern lights uses a 1 zinc and its in the coolant , they say its no longer needed . Your thoughts ? the HX core is not touching any metal do to the end boots.

[Big D]

Not all transom plates are used for grounding, some are there as anodes only.

The other thing that should be noted is that zinc is not good for the environment hence the movement to do away with them period.

There has been some call for aluminum "zincs "in salt water in some states . I have a set for my boats running gear . But I have not switched as I have none for the Engines or gen and you not suppose to mix them . And wonder about using them when every one else is using real zinc .


Big D . My Northern lights uses a 1 zinc and its in the coolant , they say its no longer needed . Your thoughts ? the HX core is not touching any metal do to the end boots.

Under the right conditions, I don't worry too much about that type of zinc use, can't hurt using it unless you don't check/maintain it if you do use one. If they're saying you don't need them then they've taken dissimilar metal consequences into consideration. As we know, there are alot of heat exchangers with anodes in them on the raw water side and that's great but if you don't check/maintain them they can cause problems when they break apart inside. Another benefit to using magnesium in that type of application (if you can find it) is that if it does break apart before you get to it, the pieces will disolve much much faster than zinc (fresh water).

Paul, on the aluminum anodes, I've included a copy of my PM to you for the benefit of others.......

I actually considered aluminum a couple of years ago and will likely be moving all my services over to that eventually given that they have made some changes to metal content recently. The only problem so far is that they don't seem to be producing a full spectrum for all applications yet so if you wanted to switch a boat over, you might get part of it done but not find the right size in aluminum for shafts for example. Can't mix two different metal anodes so my hands are tied for now. I'm keeping an eye on aluminum availability but until then it's magnesium around here.

Totally agree with the comment about some States heading into banning the use of zinc, I've heard that too some time ago. It's just a matter of time.